Collapsible cart

ABSTRACT

Described is a collapsible cart that provides substantial stability when operated. Enlarged inflatable or compliant rear wheels allow an operator to lift a front end of the cart to traverse rough surfaces as needed. Enlarged rear wheels are mounted outside an overhead profile of the collapsible cart thereby providing lateral and other stability. A first shelf, bucket or working surface may be collapsed to contact or mate with a second such shelf to create an easily transportable or storable collapsed structure. A telescoping handle allows a collapsed cart to serve as a hand dolly.

FIELD OF INVENTION

The present invention relates to carts.

BACKGROUND

Known four-wheeled carts are excessively heavy and excessively bulky.Further, these carts are often not collapsible or easily disassembledfor transportation. For example, known four wheeled carts are not easilytransported in land vehicles and airplanes where the bulk of the cartdisplaces valuable space needed for equipment storage.

Further, known four-wheeled carts are assembled with a relatively smallcastor wheel directly under each corner of the cart. This configurationmakes the cart unstable or top-heavy, especially during movement of thecart such as when a castor wheel impacts a small object or when the cartis taken over a step, curb or uneven ground. Known four-wheeled cartsalso cannot effectively move across outdoor surfaces such as a lawn,deck or uneven sidewalk. In addition, known four-wheeled carts cannoteasily negotiate stairs either in a collapsed state or in an assembledstate.

When known carts are in a collapsed or disassembled state, the carts areno longer operational. Thus, known collapsed carts serve no otherpurpose than to be treated as objects to be placed into storage orloaded for transportation.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key or essentialfeatures of the claimed subject matter, and it is not intended to beused to limit the scope of the claimed subject matter.

One aspect of the present invention provides for collapsible legsbetween a first shelf or working surface and a second shelf or workingsurface of a cart. While two shelves or working surfaces are described,it is understood that any number and configuration of shelves or workingsurfaces may be used consistent with the principles disclosed herein.Further, while four legs are shown in the Figures and described herein,any number of collapsible legs is possible. If two or more collapsiblelegs are available, the extension of less than all of the legs mayprovide an inclined shelf or working surface.

Another aspect of the present invention provides for at least one pairof wheels mounted outside the profile of a first or bottom shelf of thecart. Such mounting provides increased stability and improvedtransportability to the cart. In a preferred implementation, such wheelsare inflatable. If just one pair of inflatable wheels is used, thesewheels are placed at the rear of the cart. The inflatable wheels may belarger than traditionally sized castor wheels. The inflatable wheelsprovide a means for the cart to be used as a hand dolly when the cart isin a collapsed configuration.

In an optional aspect of the present invention, at least one pair ofcastor wheels can be adjustably swiveled and locked into a configurationoutside the profile of the cart. The swiveling of the castor wheelsprovides for increased lateral stability to the cart when desired.

In another optional aspect of the present invention, a handle providesfor a means to use the cart as a hand dolly. In a preferred aspect, ahandle can be telescoped or reversibly lengthened for increased leverageand improved maneuverability of the cart.

These and other aspects of the invention are described further in theDetailed Description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the subject matter are setforth in the appended claims. Throughout, like numerals refer to likeparts with the first digit of each numeral generally referring to thefigure which first illustrates the particular part. The subject matterand one or more preferred modes of use are best understood by referenceto the following Detailed Description of illustrative implementationswhen read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side perspective view of a collapsible cart in an extendedconfiguration according to a first exemplary implementation;

FIG. 2 is a perspective view of a collapsible cart in a partiallycollapsed configuration according to the first exemplary implementationshown in FIG. 1;

FIG. 3 is perspective view of a collapsible cart in a partiallycollapsed configuration according to a second exemplary implementationwhere one or more collapsible legs operate by sliding a pin or otherimplement in a groove or slot;

FIG. 4 is a close up of a pin and groove mechanism for collapsing orextending any of the collapsible legs shown in shown in FIG. 3;

FIG. 5 is a perspective view of a collapsible cart in a partiallyextended configuration according to a third exemplary implementation;

FIG. 6 is a perspective view of a collapsible cart in a collapsedconfiguration according to a fourth exemplary implementation;

FIG. 7 is an overhead view of a collapsible cart according to a fourthexemplary implementation;

FIG. 8 is a perspective view of a collapsible cart according to a fifthexemplary implementation;

FIG. 9 is a perspective view of the collapsible cart shown in FIG. 8 andin a collapsed state;

FIG. 10 is a perspective view of a collapsible cart according to a sixthexemplary implementation;

FIG. 11 is a perspective view of a collapsible cart according to aseventh exemplary implementation;

FIG. 12 is a perspective view of a collapsible cart in an extended stateaccording to an eighth exemplary implementation; and

FIG. 13 is a perspective close-up view of a knee joint for animplementation of a collapsible leg for a collapsible cart, analternative joint to the one shown in FIG. 1 and FIG. 2.

DETAILED DESCRIPTION

While the invention is described below with respect to one or morepreferred implementations, other implementations are possible. Theconcepts disclosed herein apply equally to other devices fortransporting bulk materials. Furthermore, the concepts applied hereinapply more generally to carts, dollies and trucks. The invention isdescribed below with reference to the accompanying figures.

While various forms and types of carts, dollies and trucks have beencreated to transport goods, all of them have failed to adequatelyaddress some basic functionalities provided by the variousimplementations of a collapsible cart described herein. Thus, there hasbeen a need for a collapsible utility cart that can overcome various andknown shortcomings.

The implementations described herein are advantageous to many types ofusers including trade show vendors, painters, home repairers,electricians, contractors, yard workers, mechanics and others who needto transport materials and to those users who would like a portableworking surface. The implementations of a collapsible or foldable cartdescribed herein can provide significantly improved time savings andutility over known carts. Several examples are illustrative. Knownutility carts, especially those marketed to consumers, cannot providesufficient lateral stability and a working surface about waist high toaccept and transport, for example, a large television or box. Knownutility carts do not fit into a car trunk. Known utility carts do nottravel easily onto a porch and over a door sill, especially when ladenwith a substantially heavy or bulky load.

FIG. 1 shows a side perspective view of a collapsible cart in anextended configuration and according to a first exemplaryimplementation. With reference to FIG. 1, a collapsible cart 100comprises a first shelf 102 and a second shelf 104 separated bycollapsible legs 106. A shelf is comprised of various features such as aworking surface 108, raised sides 110, a rolled lip 112, one or moreworking apertures 114 in the rolled lip 112 and one or more drain holes116. A working surface 108 may be smooth, textured, corrugated,flexible, rigid, or a lattice or formed into a net-like configuration ormade of such material. Drain holes 116 or other openings may beeffective in allowing liquids (e.g. rain water) to exit the shelfwithout allowing a vast majority of items (not shown) to leave theworking surface 108 and thus preventing the items from getting lost orsoiled. The raised sides 110 may also have vertical working apertures118. The raised sides 110 may be of any height 120. The height 120 of araised side 110 of a first shelf 102 may be the same or different fromthe height 120 of a raised side 110 of a second shelf 104 or other shelfor other working surface of a cart 100. In one implementation, theraised sides 110 may be vertically adjusted relative to the workingsurface 108 by a side raising, lowering or adjusting mechanism (notshown in FIG. 1, but for example, is comprised of a mounted sprocket anda series of teeth or grating in the raised sides). Such a side adjustingmechanism preferably does not interfere with stacking or mating of afirst shelf 102 to a second shelf 104.

A first shelf 102 and a second shelf 104 may have one or more featuresthat can provide locking or increased engaging of the two shelves suchthat the two shelves are less likely to move relative to one anotherwhen the collapsible cart 100 is in a fully or partially collapsedstate. For example, as shown in FIG. 1, a second shelf 104 has anengagement tab 122 at the bottom edge of a raised side 110. Theengagement tab 122 of the second shelf 104 may fit into an engagementgroove or slot 124 in the rolled lip 112 of the vertical side of thefirst shelf 102 when the cart 100 is in a collapsed state. To encouragethe shelves to stay engaged with each other when the cart 100 iscollapsed, each engagement tab 122 may comprise a spring-loaded balllatch 126. Other mechanisms may be used in association with anengagement tab 122 such as a pin through a hole (not shown) in theengagement tab.

Collapsible legs 106 are each comprised of one or more segments 128. Inthe implementation shown in FIG. 1, each collapsible leg 106 iscomprised of two segments 128 and each segment is attached to a shelf ata leg bracket 130. Each collapsible leg 106 is hinged near its middlewith a bolt 132 or other flexible or bendable joint. In theimplementation shown in FIG. 1, each collapsible leg 106 has aspring-loaded latch 134 that keeps each leg 106 extended until a userdesires to collapse the leg 106. Alternatively, instead of aspring-loaded latch 134, a collapsible leg 106 may be kept in anextended orientation by a removable pin or other mechanism.

With reference to FIG. 1, each back wheel 136 is mounted or constructedto operate outside the raised sides 110 of a first shelf or workingsurface 102 or outside the profile of the first shelf 102. Inalternative implementations, each back or rear wheel 136 may be foldedor extended to a fixed position outside the raised sides 110 of a firstshelf 102. In a preferred implementation, each back wheel 136 isinflatable, rubbery or otherwise made of a relatively compliantmaterial. The back wheel axis or axel 138 may be above, within or belowa first shelf 102. In an optional implementation, a pair of back or rearwheels 136 is mounted on an axel (not shown). In another implementation,each back wheel 136 is mounted on its own support structure so as tooperate independently of the other back wheel 136. Optionally, each backwheel 136 is provided with a damping mechanism or shock absorbingmechanism such as, but not limited to, a spring, a leaf spring, orhydraulic shock absorber.

Inflatable back wheels 136 placed outside the profile of a first shelf102 (as the cart is viewed from overhead) provide the cart 100 increasedlateral stability as compared to previously known carts. The increasedsize, type and location of the back wheels 136 improve lateralstability, especially when a substantial load is placed in or on thesecond shelf 104 and a lateral force is applied to the cart 100.Further, the size and location of the back wheels 136 enable the frontof the cart 100 to be raised from the ground or traveling surface andallow an operator to move the cart over a dramatically increased numberand types of traveling surfaces as compared to known carts. For example,the cart 100 may then travel relatively easily, even while loaded, overlawns, doorframes, door sills, rough ground, gravel surfaces, curbs, andearthen fields. The cart 100 may even be able to negotiate stairs andother previously non-negotiable areas when the collapsible legs 106 arepartially or fully extended while the cart 100 rides completely orpartially on its back wheels 136. When a cart 100 as described hereinarrives at a work site, the second shelf 104 provides an improvedworking surface for users, a place to set tools and lay out materials.

In FIG. 1, the front wheels 140 are shown inside the profile of thefirst shelf 102 or under the first shelf 102. However, in otherimplementations, to provide increased stability, the front wheels 140may be mounted individually or on an axel which is outside the profileof the first shelf 102 (as seen from above) thereby providing additionalincreased stability including increased lateral stability.

In an implementation of a collapsible cart, the front wheels 140 areswivel castor wheels that can swivel in a plane generally parallel withthe traveling surface (x-y plane). In a preferred implementation, thefront of the cart 100 is slightly lower relative to the back of the cart100 since the height of the front wheels 140 (or the combination offront wheels 140 and accompanying mounting elements) is shorter than theeffective height of the back wheels 136. This configuration provides atendency for a cart operator to slightly lift the front wheels 140 fromthe traveling surface upon the cart 100 receiving a first impulse offorce in a forward direction (toward the front wheels 140) or rearwarddirection (toward the back wheels 136). In this way, any load on thefront wheels 140 is reduced when the cart 100 first begins its motion.At this start of motion, a collapsible cart 100 is operating strongly onits rear wheels 136 such that the load on the collapsible cart 100 isprimarily on the back wheels 136. Such operation provides an improved orsmoother lateral, pivotal or forward motion or ride to the collapsiblecart 100. In an optional implementation, the front wheels 140 maycomprise a suspension mechanism 142 to reduce the impact of uneventraveling surfaces on the cart 100 and to items (not shown) in the cart100.

The cart 100 may comprise a handle 144 and may comprise a utility bar146. In a preferred implementation, the handle 144 is attached to orforms part of the second shelf 104. The utility bar 146 may be mountedin a utility region 148 between the handle 144 and the second shelf 104.In an optional implementation, a toolbox or container is speciallyshaped to securely lodge or lock into the utility region 148. Such acontainer (not shown) provides a location for relatively smaller itemsto be transported and allows the second shelf 104 to serve moreproductively as a working surface when an operator uses the cart as araised working surface.

FIG. 2 is a perspective view of a collapsible cart according to thefirst exemplary implementation shown in FIG. 1 and in a partiallycollapsed configuration. With reference to FIG. 2, each collapsible leg106 of a back pair of collapsible legs is nearly fully collapsed. Asshown, each collapsible leg 106 is hinged in its center region. In theimplementation shown in FIG. 2, each collapsible leg 106 collapsestoward the interior of the first shelf 102. Each of the frontcollapsible legs 106 may similarly be placed into a collapsed state suchthat each of these legs collapses toward the interior of the cart 100. Afront collapsible leg 106 is offset from a corresponding backcollapsible leg 106 such that when both of such collapsible legs 106 arein a collapsed state, the collapsed collapsible legs 106 do notinterfere with or otherwise impact one another. In some implementations,a front collapsible leg and a rear collapsible leg may overlap eachother or otherwise stack on top of one another when both are in apartial or fully collapsed state.

A close-up view of a collapsible leg 106 shows, in one exemplaryimplementation, that a collapsible leg comprises a bolt 132, a nut 232and a spring-loaded latch 134. The spring-loaded latch 134 is amechanism to releasably lock and maintain a collapsible leg 106 in anextended position. Other implementations of a releasable lock arepossible such a second bolt and threaded nut. One such implementation isshown in FIG. 13. In a preferred implementation, a collapsible leg 106may be reversibly locked in one or more partially extended state or in afully extended state or position.

With reference to FIG. 2, the second shelf 104 provides an inclinedworking surface that may provide an improved working surface as comparedto other carts, dollies and trucks. While not shown in FIG. 2, each ofthe collapsible legs 106 may be independently adjusted to a full orpartially extended position thereby allowing an operator to select anyof a plurality of orientations for a second shelf 104 relative to afirst shelf 102 or relative to the surface on which the collapsible cart100 rests or travels.

In one implementation, a width 202 of a first shelf 102 is preferablybetween 16 and 24 inches, but may be of any dimension. The width 202 ofthe first shelf 102 may be smaller than, the same as, or greater than awidth of a second shelf 104. A length 204 of the first shelf 102 ispreferably between 26 and 48 inches, but may be of any dimension. Thelength 204 of the first shelf 102 may be smaller than, the same as, orgreater than a length of a second shelf 104.

A height 236 of each of the rear wheels 136 may be of any dimension. Ina preferred implementation, the height 236 of each of the rear wheels136 is between about 6 and about 15 inches. A height 240 of each of thefront wheels 140 may be of any dimension. In a preferred implementation,the height 240 of each of the front wheels 140 is between about 2 andabout 12 inches. For a particular construction of a cart, a height 236of the rear wheels 136 and a height 240 of the front wheels 140 may eachbe selected such that a plane defining the first shelf 102 is inclinedtoward the front of the cart 100, relatively level or parallel with atraveling surface, or inclined toward the rear of the cart 100. Inanother implementation, the height of the rear wheels 136 and a heightof the front wheels 140, for each wheel, may be independently adjustedor selected by a cart operator.

A width 212 of a rolled edge of a first shelf 102 and a width 212 of arolled edge of a second shelf may be of any dimension. The width 212 ofa rolled edge may depend upon the material used to make the shelf or maybe selected to enable or facilitate one or more features in the rollededge of the shelf.

FIG. 3 is perspective view of a collapsible cart 300 in a partiallycollapsed configuration according to a second exemplary implementation.With reference to FIG. 3, the second exemplary implementation comprisescollapsible legs 306. Each collapsible leg 306 comprises a bolt, peg orroller 308. One or both ends of each collapsible leg 306 slide in aslotted bracket, groove or slot 302. The slotted bracket, groove or slot302 is attached to, formed in, or forms part of a shelf. FIG. 3 showscollapsible legs 306 where only a single end of each collapsible leg 306slides in a slotted bracket 302. In the implementation shown in FIG. 3,the front collapsible legs 306 are each mounted to a leg bracket 130 ofa first shelf 102 and the rear collapsible legs 306 are each mounted toa leg bracket 130 of a second shelf 104. Each slotted bracket, groove orslot 302 may comprise one or more recesses, a marking, a bolt, a pin, anut or other feature 304 that can serve as a stopper or a stoppinglocation for a bolt, peg or roller 308. In a preferred implementation ofcollapsible cart 300, a front collapsible leg 306 is attached to a legbracket 130 on a shelf and slides in a bracket, groove or slot 302mounted to or forming part of another shelf.

The second exemplary implementation of a collapsible cart 300 comprisesan extendable front wheel bracket 310 for each front wheel 140. Eachfront wheel 140 is mounted with one or more mounting fasteners 312. Eachfront wheel bracket 310 may be extended toward the front of the cart 300and may be rotated to a lateral side of the cart 300 (once extendedtoward the front of the cart 300) or may be directly extended toward alateral side of the cart 300. Each front wheel bracket 310 may bereversibly locked into place. The extendable front wheels 140 then canprovide increased stability to the cart 300. Each front wheel bracket310 comprises a suspension mechanism 142 to reduce the impact of uneventraveling surfaces on the cart 300.

FIG. 4 is a close up of a pin and groove mechanism for collapsing orextending any of the collapsible legs 306 shown in shown in FIG. 3. Withreference to FIG. 4, a pin 308 comprises a wheel 408 that rolls back andforth in a groove 302. The wheel 408 and a washer 416 facilitate slidingor movement of the collapsible leg 306 in the groove 302. A threaded nut414 fastens the pin 308 to the collapsible leg 306. The pin and groovemechanism is one of many possible mechanisms for allowing a collapsiblecart to be taken between an extended state and a collapsed state. Incertain implementations, a collapsible cart may be placed in partiallycollapsed and operational state.

FIG. 5 is a perspective view of a collapsible cart in a partiallycollapsed or partially extended configuration or state according to athird exemplary implementation. With reference to FIG. 5, a frontcollapsible leg 306A and a corresponding wheel 408A slide along one sideof a doubly grooved track 502 and a back collapsible leg 306B and acorresponding wheel 408B slide along an opposing side of the doublygrooved track 502. In this particular implementation, a doubly groovedtrack 502 provides for a simplified construction and ensuring smoothoperation as an operator collapses or extends the collapsible legs.Depending on geometry, mechanism or implementation of collapsible leg,each collapsible leg may be independently extended, collapsed orpositioned.

FIG. 6 is a perspective view of a collapsible cart 600 in a collapsedconfiguration according to a fourth exemplary implementation. Withreference to FIG. 6, a handle 144 comprises an extendable arm 602. Theextendable arm 602 is slidably extendible along or over a base arm 604.The extendable arm 602 comprises a spring-loaded ball latch 606. Thespring-loaded ball latch 606 of the extendable arm 602 facilitatesplacing the handle 144 in one of several available handle positions.Extending the handle 144 changes the distance 608 between the handle 144the second shelf 104. When the extendible arm 602 and handle 144 are inan extended position, an operator has relatively more leverage to liftand rotate the cart 600 about the axis defined by the back wheel axeland axis 138 than when the handle 144 is collapsed.

With reference to FIG. 6, working apertures 114 in the second shelf 104are exposed and may be used when the cart 600 is in a collapsed state.For example, an operator or user could stretch an elastic cord over oneor more items (not shown) on or in the recess of the second shelf orworking surface 104. FIG. 6 shows an engagement tab 122 protrudingthrough an engagement slot 124 in a rolled edge of a raised side 110 ofthe bottom or first shelf 102. A spring-loaded ball latch 126 of theengagement tab 122 is engaged such that the top or second cart shelf 104tends to remain mated to the first cart shelf 102. Other mechanismsother than an engagement tab 122 are possible. When in such a collapsedstate, the collapsible cart 600 is easily stored and transported. Forexample, the collapsed collapsible cart 600 may be placed inside a cartrunk, placed in the bed of a truck, or hooked on the side of a utilitytruck or other vehicle. In a collapsed state, a collapsible cart 600 ismore easily handled and transported.

A collapsible cart 600 comprises a handcart plate. In an examplaryimplementation, and with reference to FIG. 6, a handcart plate 620 isreversibly engaged in one or more plate slots 628. Plate tabs 622protrude through plate tab apertures (not shown). A spring-loaded balllatch 626 in one or more plate tabs 622 encourages the handcart plate620 to remain in a relatively fixed position in the cart 600. When thehandcart plate 620 is engaged in the cart 600, the cart 600 may be usedsimilarly to a two-wheeled handcart or hand dolly instead of afour-wheeled cart. The handcart or hand dolly functionality is enhancedwhen the handle 144 is extended. The cart 600 is then more easilynegotiated over uneven surfaces such as stairs, lawns, and constructionsites.

A collapsible cart as described herein can serve many functions. Forexample, with reference to FIG. 6, in an optional implementation, anextendible rail 630 is available to extend or protrude from the back ofthe second shelf 104. One or more rail brackets 632 provide support toeach extendible rail 630. An extendible rail 630 may serve a variety ofpurposes such as, but not limited to, a sawhorse and a support foranchoring a clamp or vise.

FIG. 7 is an overhead view of a collapsible cart according to a fourthexemplary implementation shown in FIG. 6. With reference to FIG. 7, asecond shelf 104 is visible over the top of a first shelf (not shown).The two rear wheels 136 are outside the profile or perimeter of at leastthe first shelf and preferably outside the profile of the second shelf104. A panel 702 is visible in each of the corners of the second shelf104. The panel 702 comprises one or more fasteners 704 for a doublygrooved track (shown in FIG. 5) or for a leg bracket (viz. FIG. 3). Thefastener 704 may be a screw, bolt or some other feature. The fastener704 may be of any shape or configuration. The fastener 704 is only shownas a circular structure in FIG. 7 for illustrative purposes only. Forsimplicity of illustration, a handcart plate 620 and correspondingfeatures are not shown in FIG. 7.

FIG. 8 is a perspective view of a collapsible or foldable cart 800according to a fifth exemplary implementation. With reference to FIG. 8,in this exemplary implementation, a release mechanism 802 disengagesfrom or releases a front leg or set of front foldable legs 804. In anexemplary implementation, the front leg is U-shaped. To collapse or foldthis implementation of a collapsible cart 800, a series of steps isperformed. A front leg 804 (or set of front foldable legs) is foldeddownward until it fits inside or proximal to a first shelf or workingsurface 102. Next, the front leg 804 pivots around a front set of pivotpoints 808 located in or near a front end of a first shelf or workingsurface 102. Optionally, if present, a handle (not shown) is removedfrom, folded into, or otherwise rotated or pivoted close to the secondshelf or working surface 104. Subsequently, the second or top shelf orworking surface 104 may be pivoted around a set of top pivot points 810until the second or top shelf 104 is aligned with the back or rear legs806. Next, the first or bottom shelf 102 may be rotated or pivotedaround a set of rear or lower pivot points 812. In FIG. 8, the lowerpivot points 812 are shown to comprise a bolt, rivet or pin through anaperture of a rear leg 806. However, other implementations of a pivotpoint 812 are possible.

In a preferred implementation, the length 814 of the second shelf 104 issmaller than the height 816 of the rear legs 806, although in otherimplementations, the second shelf 104 and the first shelf 102 may be ofany shape, size or dimension consistent with functionality or utilitydisclosed herein. A handle distance 818 plus the length 814 of the topor second shelf 104 are preferably less than the height 816 of the rearlegs 806 thereby removing the need to remove, pivot or change theposition or orientation of a handle (not shown) before pivoting the topor second shelf 104 to align or pivot to be near the rear legs 806.

With reference to FIG. 8, although the U-shaped front leg 804 is shownmounted near an extreme end of the first shelf 102, and mounted to thefirst shelf 102, the U-shaped front leg bracket 804 may be located ormounted on either shelf or on another structure, and may be located atany point generally along a plane defined by one of the shelves. Oncecollapsed, the cart 800 may be moved, handled or manipulated by a secondhandle (not shown), which is preferably located or attached near thesecond shelf 104 and located generally above the rear wheels 136. As inother embodiments, once the collapsible or foldable cart 800 iscollapsed, the foldable cart 800 may be operated or manipulated like adolly or handcart.

FIG. 9 shows a perspective view of the collapsible cart 800 shown inFIG. 8 in a collapsed state and with a handle 820. With reference toFIG. 9, the first shelf 102 and the second shelf 104 are placed or matedtogether in a face-to-face or top-to-top orientation such that a hollowrecess is formed between the two. When mated together, the shelves aremechanically encouraged to stay together with a spring-loaded ball latchon each of one or more tabs where each tab is inserted in a respectiveslot or opening (not shown in FIG. 9, but mechanism shown in FIG. 6). Asecond handle 820 in a collapsed, extended or other state allows anoperator to easily move and manipulate the collapsed cart. (Forsimplicity of illustration, a second handle 820 is not shown in FIG. 8.)

In an exemplary implementation, the size or profile of a first shelf 102is different from or complimentary to that of a second shelf 104 suchthat a first shelf 102 may be nested or recessed in the second shelf104. The combined height 902 of the two shelves may thus be reduced. Ina preferred implementation, the combined height 902 of the two shelvesallows an operator to wheel the collapsed cart 800 with either the firstshelf 102 or the second shelf 104 being closer to the ground ortraveling surface. A second handle 820 may be extended to allow anoperator to more easily handle the collapsed cart 800 and to treat orwork with the collapsed cart 800 more like a dolly or handcart than atraditional, rigid cart.

FIG. 10 is a perspective view of a collapsible cart according to a sixthexemplary implementation. With reference to FIG. 10, a collapsible cart1000 comprises collapsible legs each with a single leg segment 1028.Each leg segment 1028 is connected to one other leg segment 1028 in ascissor-like arrangement. This arrangement allows for at least one endof each leg segment 1028 to travel in a slot or channel 1030 and foreach pair of legs (e.g. a front leg and a back leg) to operate like ascissor. The slot or channel 1030 is shown in FIG. 10 under a secondshelf 104, but the slot or channel 1030 may be formed in or attached toa first shelf 102. The scissor-like arrangement of collapsible leg isanother implementation of collapsible leg mechanism that may be used inthe invention. While the scissor mechanism is shown with a front leg anda back leg forming a scissor-like arrangement, two front legs or twoback legs may form the scissor-like arrangement.

FIG. 11 is a perspective view of a collapsible cart according to aseventh exemplary implementation. With reference to FIG. 11, to collapsethis implementation of a collapsible cart 1100, a series of steps isperformed. First, an engagement mechanism (not shown) is released suchthat a second shelf 1104 is no longer locked or reversibly fixed to eachof leg 1106. For example, an engagement mechanism comprises aspring-loaded bolt, one for each leg 1106. In such case, eachspring-loaded bolt is disengaged, one from each corner of the secondshelf 1104 corresponding to a respective leg 1106. Next, the secondshelf 1104 is lowered and nested or rested against a first shelf 1102.In one implementation, a spring-loaded bolt 1110 slides in a groove 1108inside a cart leg 1106. Other implementations are possible. In apreferred implementation, the cart legs 1106 are reversibly connected toa first shelf 1102 and a second shelf 1104 and are merely separate partsof an assembled cart. To complete the series of steps to collapse thecart 1100, each cart leg 1106 is rotated into or against the secondshelf 1104. In an alternative implementation, each cart leg 1106 may berotated 270 degrees and placed against, near or adjacent to the firstshelf 1102. Once collapsed, the cart 1100 may be further moved, handled,manipulated or stored.

FIG. 12 is a perspective view of a collapsible cart 1200 in an extendedstate according to an eighth exemplary implementation. With reference toFIG. 12, a collapsible cart 1200 comprises a support section 1202. Asupport section 1202 comprises one or more shelf support cross members1208, a leg adjustment section 1210, one or more support members 1232,and one or more hinges or loops 1234. The shelf support members 1208 maybe fastened or formed together and are fastened (either permanently,temporarily or removably) to one of the shelves or working surfaces. InFIG. 12, the top or second shelf or working surface 104 is shownattached to the shelf support members 1208 and the two (working surfaceand support members) are attached together by fasteners 1236.

A movable or collapsible cart leg 1204 at its proximal end 1212 isrotatably attached with a pin 1206 in a hinge or bracket 1234. A nut orother fastener may be used in conjunction with the pin 1206 and hinge orbracket 1234. At its distal end 1214, the movable cart leg 1204 ispreferably not directly fixed to the support section 1202. The movablecart legs are each slidably engaged in the leg adjustment section 1210.In one implementation, the leg adjustment section 1210 comprises a firstrail 1252, a second rail 1254, and a third rail 1256. The first rail1252 and the second rail 1254 form a slot or track 1218B in which adistal end of each rear leg 1204 may slide when the collapsible cart1200 is placed into a collapsed state. Similarly, the second rail 1254and the third rail 1256 form a slot or track 1218A in which the distalend of each front leg 1204 may slide when the collapsible cart 1200 isplaced into a collapsed state. A cross beam or rail 1258, preferably oneon each end of the leg adjustment section 1210, provides stability andstrength to the leg adjustment section 1210. Vertical support members1260 may be used to brace the rails 1252, 1254 and 1256. Alternatively,instead of three rails, the side portions of the leg adjustment section1210 may be formed from a solid block of metal and the leg adjustmentsection 1210 may not comprise vertical support members 1260.

A cross member 1216 connects distal ends 1214 of two movable cart legs1204, one connecting the front pair of movable cart legs 1204 and onecross member 1216 connecting the rear pair of movable cart legs 1204. Asthe second shelf 104 is extended or raised relative to a first shelf102, the cross member 1216 may contact, stick to or engage in ridges,grooves or depressions (not shown) in a corresponding slot, track orchannel 1218A, 1218B. In this way, the cross member 1216 may take stepsas the second shelf 104 is ratcheted or gradually raised or extendedupward, or gradually lowered or compressed toward the first shelf 102downward. A support arm provides additional support and stability toeach movable cart leg 1204. A support arm is rotatably attached to amovable cart leg 1204 at a pivot point 1224 in a cart leg 1204. Theother end 1226 of the support arm is rotatably attached to or near theleg adjustment section 1210.

The movable cart legs 1204 and second shelf 104 may be held in acollapsed state by a lock mechanism 1228. In one implementation, thelock mechanism 1228 comprises a shelf locking arm 1242, a leg lockingarm 1244 and a lever 1246. A shelf locking arm 1242 reversibly engages,for example, a second shelf 104 when the collapsible cart 1200 is in acollapsed state. A leg locking arm 1244 holds or forces one or morecross members 1216 toward a maximally extended position such that thecart 1200 may be loaded without fear of the cart legs 1204 moving ontheir own. The lock mechanism may be spring loaded so as to facilitateremovably engaging either a shelf, or a cross member 1216 or collapsibleleg 1204 or other part comprising the support section 1202.

The support section 1202 may be fixedly or removably attached to one orboth of the two shelves. In one implementation, the support section 1202nests inside a first shelf 102 or inside a second shelf 104 when thecollapsible cart 1200 is in a collapsed state. Alternatively, thesupport may reside between the two shelves 102, 104 such that the legadjustment section 1210 rests on or near or in between one of theshelves 102, 104. Alternatively, the support section 1202, when the cartis collapsed, may be removed from the shelves 102, 104 and stored insideor to one or more of the shelves 102, 104 for convenience. Preferably,the support section collapses and takes up minimal vertical space whenthe collapsible cart 1200 is in a collapsed state.

FIG. 13 is a perspective close-up view of one implementation of a kneejoint 1300 for an implementation of a collapsible leg for a collapsiblecart, an alternative joint to the one shown in FIG. 1 and FIG. 2. Theelements comprising FIG. 13 are not drawn to scale and are shown forpurposes of illustration only. With reference to FIG. 13, a tang 1302 ofan upper leg segment 1304 is reversibly inserted into a recess 1306 in alower leg segment 1308. When the upper leg segment 1304 and the lowerleg segment 1308 are properly aligned, a spring-loaded ball lock 1310engages an opening or ball recess 1312 in the lower leg segment 1308.The upper leg segment 1306 and lower leg segment 1308 are eachpreferably of a rectangular or square cross-section. Such leg segmentsprovide for strong lateral stability, yet can be relatively lightweightfor use with a collapsible and useful cart. In one implementation, aknee joint 1300 is comprised of a hinge pin or hinge axis 1314 aroundwhich rotate hinge tabs 1316. One or more corresponding hinge tabs 1316are affixed (by welding, glue or other means) to either an upper legsegment 1304 or a lower leg segment 1308.

The foregoing discussion has been presented for purposes of illustrationand description. Various features from one implementation can becombined with other features from other implementations. The descriptionis not intended to limit the invention to the form or forms disclosedherein. Consequently, variation and modification commensurate with theabove teachings, within the skill and knowledge of the relevant art, arewithin the scope of the present invention. The implementations describedherein and above are further intended to explain the best mode presentlyknown of practicing the invention and to enable others skilled in theart to use the invention as such, or in other implementations, and withthe various modifications required by their particular application oruses of the invention. It is intended that the appended claims beconstrued to include alternate implementations to the extent permitted.

We claim:
 1. A collapsible cart comprising: a first pair of wheels; asecond pair of wheels, wherein each of the first pair of wheels islarger in diameter than each of the second pair of wheels; a firstworking surface, wherein the first working surface comprises an outerprofile, wherein each of the first pair of wheels is mounted outside theouter profile of the first working surface; at least one collapsibleleg, wherein each collapsible leg is extendable to at least one extendedposition; a second working surface, wherein the second working surfacecomprises a slot running substantially parallel with either the firstworking surface or the second working surface, wherein the slot engagesone end of the at least one collapsible leg.
 2. The collapsible cart ofclaim 1 wherein a profile of each collapsible leg fits within the outerprofile of the first working surface when the collapsible leg is in acollapsed state.
 3. The collapsible cart of claim 1, wherein eachcollapsible leg includes a release mechanism, wherein when the releasemechanism is engaged, the collapsible leg becomes placeable into acollapsed state.
 4. The collapsible cart of claim 1, wherein thecollapsible cart further comprises: a leg bracket for each collapsibleleg, wherein another end of at least one of the said at least onecollapsible leg is fixed in a respective leg bracket.
 5. The collapsiblecart of claim 1 wherein the collapsible cart further comprises: atelescoping handle.
 6. The collapsible cart of claim 1 wherein thecollapsible cart further comprises: a means for securing the firstworking surface near the second working surface when the collapsiblecart is in a collapsed state.
 7. The collapsible cart of claim 1,wherein each of the first pair of wheels is pliant, and wherein thefirst pair of wheels define a rear wheel axis.
 8. The collapsible cartof claim 1, wherein the collapsible cart further comprises: a supportarm for each respective collapsible leg.
 9. The collapsible cart ofclaim 8, wherein each support arm is reversibly lockable in one ofmultiple positions.
 10. The collapsible cart of claim 1 wherein aprofile of at least one of the said at least one collapsible leg fitssubstantially outside an outer profile of the second working surfacewhen the at least one collapsible leg is in a collapsed state.
 11. Thecollapsible cart of claim 1 wherein a profile of at least one of thesaid at least one collapsible leg fits substantially inside an outerprofile of the second working surface when the at least one collapsibleleg is in a collapsed state.
 12. The collapsible cart of claim 1,wherein the collapsible cart comprises four collapsible legs, whereinthe first working surface comprises two slots, wherein the secondworking surface comprises two slots, and wherein two of the collapsiblelegs are engaged with a respective slot of the second working surfaceand the other two collapsible legs are engaged with a respective slot ofthe first working surface.
 13. The collapsible cart of claim 1, whereinthe collapsible cart comprises four collapsible legs, wherein the firstworking surface comprises two slots, and wherein two of the collapsiblelegs are engaged with a respective slot of the first working surface.14. The collapsible cart of claim 1, wherein each of the second pair ofwheels are extendable outside the outer profile of the first workingsurface.
 15. A collapsible cart comprising: a first pair of wheels; asecond pair of wheels, wherein each of the first pair of wheels islarger in diameter than each of the second pair of wheels; a firstshelf, wherein the first shelf includes a profile, wherein each of thefirst pair of wheels is mounted outside the outer profile of the firstshelf; collapsible legs, wherein each collapsible leg is extendable toat least one extended position; a second shelf, wherein the second shelfincludes a profile, wherein either the first shelf or second shelfincludes a slot running substantially parallel with either the firstshelf or the second shelf, wherein the slot engages one end of at leastone of the collapsible legs.
 16. The collapsible cart of claim 15wherein a profile of at least one of the said collapsible legs fitssubstantially inside the profile of the first working surface and insidethe profile of the second working surface.
 17. The collapsible cart ofclaim 15 wherein a profile of at least one of the said collapsible legsfits substantially inside the profile of the first working surface andoutside the profile of the second working surface.
 18. The collapsiblecart of claim 15 wherein a profile of at least one of the saidcollapsible legs fits substantially outside the profile of the firstworking surface and inside the profile of the second working surface.19. The collapsible cart of claim 15 wherein a profile of at least oneof the said collapsible legs fits substantially outside the profile ofthe first working surface and outside the profile of the second workingsurface.